The invention relates to a method and to a device for quantitatively detecting the power proportion of a radiation background of a pulsed laser. The invention further relates to the use of a saturable element.
A quantification of the radiation background, in particular of the so-called continuous wave (cw) background, of a pulsed laser or laser system is of great interest both to material processors as well as to laser developers. For example, with precise knowledge of the radiation background, adverse influences of the radiation background on machining processes can be selectively examined. Also in the development of pulsed laser systems, particularly in ultra-short pulsed laser systems, is the quantitative proportion of the radiation background of great interest.
So far, the radiation background or cw background can only be inferred indirectly depending on the operating mode of the laser. In a passive mode-locked laser oscillator, it is possible to draw qualitative conclusions on the operating mode based on the spectrum, for example, i.e. it is possible to determine whether a pure pulsed operation is present or whether there is a cw ground in addition. A quantitative assessment of the power proportion of the cw background or the power ratio between pulsed proportion and cw proportion is, however, only feasible and practicable with severe limitations.
For a quantitative measurement, e.g. a photodiode could be used and the power proportion could be determined both during the pulses and in the period between the pulses by integration of the diode signal. However, this requires an extremely high dynamic range of the photodiode due to the high power of the laser radiation during the pulses and the short duration of the pulses, so that this method proves to be impracticable. Furthermore, any offsets and external light sources would cause a very large error. In addition, this method cannot be used in ultra-short pulses, since due to the limited response or decay time of the diodes a resolution of the individual pulses is no possible any more, and thus a ground actually not present would be measured by superposition of several pulses during the measurement time.
Another possible method of determining the radiation background of a pulsed laser or laser system is frequency doubling, the efficiency of which is dependent on the proportion of the pulsed power to the total power. However, the components required are expensive and the measurement is inaccurate, as several unknown parameters are included in the conversion efficiency.
The present disclosure therefore provides a device and a method for quantitatively detecting the power proportion of the radiation background or cw background of pulsed lasers or laser systems.